Dual grounds?

[Paul Perry]

At 10:31 AM 4/05/98 -0500, Mark McLemore  wrote:

>    3. If I use the dual-ground method, which ground do I attach
>       bypass capacitors to?
....I think the idea is for the analog stuff to go to the analog line,
and the digital stuff (switches, caps discharging in lfo's) to the 
digital earth
>
>    4. I used to have a problem with VCO's locking due to intermodulation
>       over the power supply lines, does the dual grounding system
>       help this problem at all?
.....probably not..... what you can do is to have a further degree of 
isolation for the lfo's by running a 330 ohm resistor to each LFO power 
input and putting a big electro AND a ceramic bypass from the LFO side to 
earth.... I had trouble with leakage from oscilators and Batz said to do
this... worked for me!

>
>    5. Does anyone see a pitfall or disaster waiting to happen by using
>       the above approach?
....no.....
>
>I'd appreciate any advice or comments from those of you with insight
>into the black magic of effective grounding.
.....there is a site somewhere with a long grounding rave, might turn up 
unde 'ground noise faq'
the point it made that I found interesting was the idea that to pick up
interference you need a LOOP circuit, and the cross section determines 
how much interference you pick up (talking inductance here) so if you run 
wires/traces close together, there is less pickup from transformer radiation etc

All I would say is use REALLY thick wire.... I have seen woven copper auto
battery wire in labs.... I solved a veroboard problem by using fat wire in
the PSU part..
>
BTW, I think it was an Analog Devices app note that said,
"Trust your mother, but never trust your ground."

paul perry melbourne australia